Ratiometric electrochemical detection of kojic acid based on glassy carbon modified MXene nanocomposite

The significance of developing a selective and sensitive sensor for quality control purposes is underscored by the prevalent use of kojic acid (KA) in cosmetics, pharmaceuticals, and food items. KA's utility stems from its ability to inhibit tyrosinase activity. However, the instability of KA and its potential adverse effects have created a pressing need for accurate and sensitive sensors capable of analyzing real samples. This research introduces an electrochemical ratiometric sensor designed to accurately detect KA in actual cosmetic and food samples. The ratiometric sensor offers distinct advantages such as enhanced selectivity, reproducibility, and sensitivity. It achieves this by leveraging the ratio between two output signals, thereby producing reliable and undistorted results. The sensor is constructed by modifying a Glassy Carbon Electrode (GCE) with a nanocomposite consisting of Ti3C2 MXene, Prussian blue, and gold nanoparticles. The incorporation of MXene and gold nanoparticles heightens sensitivity and reduces impedance. Meanwhile, the Prussian blue signal diminishes proportionally with increasing KA concentration, forming the basis for the ratiometric sensing mechanism. The outcomes of the study reveal a broad linear range (1–600 μM), a low detection limit (1 μM), and strong selectivity for KA. These findings suggest the sensor's potential efficacy in quality control across cosmetics, pharmaceuticals, and food products.

Electronic Supplementary Material (ESI) for RSC Advances.This journal is © The Royal Society of Chemistry 2023

XPS characterization of Ti 3 C 2 T x MXene
X-ray photoelectron spectroscopy (XPS) was employed to analyze the chemical composition of the assynthesized Ti 3 C 2 T x MXene.The survey spectrum of the MXene, as illustrated in Fig. S2a, confirmed the presence of Titanium, Carbon, and Oxygen, which was further supported by the EDS elemental mapping (Figure . S1). Deconvolution of the core-level spectrum of Ti 2p (Fig. S2b) revealed peaks at approximately ~454.6, ~457.6 eV, and ~459 eV corresponding to Ti-C bond, Ti 3+ , and Ti 4+ , respectively 1 .The deconvoluted spectrum of C 1s (Fig. S2c) comprised peaks centered around ~281.6, 282.4,~284.7,~286.

Optimization of the electrochemical performance
The MXene and nanoparticles loading on the modified electrode were optimized for optimal performance using impedance spectroscopy.Initially, five different MXene concentrations ranging from 1-5 mg/mL were selected for the fabrication of GCE/MXene and tested for impedance analysis.As illustrated in Fig. S6a, the results indicated an optimal MXene concentration of 4 mg/mL for decreased charge transfer resistance.Consequently, a concentration of 4 mg/mL was chosen for further modifications to the electrode.
Subsequently, the concentration of PB NPs was optimized (Fig. S6b) on GCE/MXene/PB NPs, and a concentration of 2 mg/mL was found to provide a lower impedance for the modified electrode.Similarly, the loading of AuNPs was optimized, and AuNPs loading of 2 µL was selected for the final electrode modification (Fig. S6c).Regarding Nafion, it was observed that an increase in concentration led to a drastic increase in impedance.Hence, a lower concentration of 0.1% was chosen for the fabrication of the Kojic acid sensor.
Fig. S7 A plausible mechanism for the ratiometric electrochemical sensor for Kojic acid.Adapted from 3,4 .

Real sample analysis
Real sample analysis was carried out using Kojic acid soap and apple cider vinegar.Briefly, the Kojic acid soap was ground into fine powder.0.5 g of the ground soap was transferred into a beaker and dissolved in 100 mL PBS (pH 7.4) by gentle heating.The solution was centrifuged to remove any particulate matter.pH of the solution is adjusted using dilute HCl.Known concentrations of standard Kojic acid were then introduced into the solution by the standard addition method and stored at 4 o C. Apple cider vinegar was purchased and diluted 100 times using PBS 7.4.Known concentrations of standard Kojic acid were introduced into the solution by the standard addition method and stored at 4 o C.
Fig. S1 Schematics of the Tyrosinase inhibition of Kojic acid leading to the decreased production of Melanin.

Fig
Fig. S4 HR-TEM image of Ti 3 C 2 T x MXene showing the interlayer spacing corresponding to the (0 0 2) lattice plane.